[9fans] OT: supporting multiple VGA cards (was "A shot in the dark")

[Digby Tarvin <digbyt@acm.org>]

On the subject of diagnostic tools (this is not specifically a Plan9
issue, but someone on this list might know...):

I am interested in connecting more than one graphics adapter so that
one can be dedicated to low level diagnostics (rather than the more
usual dual head user interface).. but I am not sure how the hardware
deals with that given that the VGA standard seems to imply that all
the cards would be using identical memory addresses and IO ports.
Otherwise I would expect PCI to be able to automatically
map resources to non-conflicting addresses/IO ports.

In any case my BIOS has a setting which allows selection between AGP and
PCI as 'primary' Video, suggesting that it is indeed possible to have at
least one of each.

The only thing I can think of is that perhaps the VGA/CGA/EGA etc modes
are suppressed in the non-primary card, leaving only the more advanced
and less standard mode available. But this would be less ideal, as text
mode would be more useful for low overhead diagnostics.

Does anyone know what actually happens?

Regards,
DigbyT

On Wed, May 28, 2008 at 05:31:27PM +1000, Bruce Ellis wrote:
> When I did the port to the PS2 there wasn't even a light to blink. To
> get thru l.s I discovered a register I could write that resets the
> video.
>
> Only a hundred lines (most innocent) to binary chop.
>
> Ken has a better tale of a device that only had a speaker and
> debugging by tones.
>
> brucee
>
> On 5/28/08, Paul Lalonde <plalonde@telus.net> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > FWIW, we used a similar technique just last summer debugging some PS3

--
Digby R. S. Tarvin                                          digbyt(at)digbyt.com
http://www.digbyt.com